1 Many people didn't want a war to begin. Mothers and fathers all over Europe hoped for good lives for their sons who were just becoming adults. Young men hoped to begin their adult lives by going to work, getting married, and raising families. Instead, in 1914, many of them went to war.2 Some of the leaders in Europe didn't want the war to begin either. They tried to convince others not to go to war. Instead, one country after another declared war.3 How did it happen? What caused World War I?4 There were several causes of World War I. The most immediate cause was the assassination of Archduke Francis Ferdinand of Austria-Hungary. Austria-Hungary decided that Serbia was to blame for the assassination and declared war on Serbia.